If you believe there is satan? Then there is God!
How do you know there is God? No, you don't see him with your 'naked eyes'. You see Him with the eyes of Faith!
I know, some don't believe in God. The problem is, it's not my place to say that you should believe there is God or not. It's really up to you. God, give you eyes so that you can see for yourself. Again, I can only say what I know. It's God will and He knows the truth inside yours and my heart. He knows, if I have faith in Him. He knows, if you're just saying that you believe in Him or just for the sake of showing to others or just following the crowds. It's really difficult to really describe faith.
All that we can do, is stay true to our faith. To learn what God messenger has taugth us. God, has send a whole lot of messenger to mankind. To give us warnings and also to tell about good tidings that awaits.
Believe...and He will show you the way...